1. Field of the Invention
The present invention relates to inductors, such as those used in electrical filters, and more particularly to three-phase electrical inductors.
2. Description of the Related Art
AC motors often are operated by motor drives in which both the amplitude and the frequency of the stator winding voltage are controlled to vary the rotor speed. In a normal operating mode, the motor drive switches voltage from a source to create an output voltage at a particular frequency and magnitude that is applied to drive the electric motor at a desired speed.
When the mechanism connected to the motor decelerates, the inertia of the that mechanism causes the motor to continue to rotate even if the electrical supply is disconnected. At this time, the motor acts as a generator producing electrical power while being driven by the inertia of its load. In a regenerative mode, the motor drive conducts that generated electricity from the motor to an electrical load, such as back to the supply used during normal operation. The regeneration can be used to brake the motor and its load. In other situations, the regenerative mode can be employed to recharge batteries or power other equipment connected to the same supply lines that feed the motor drive during the normal operating mode.
Electrical filters are often placed between the electric utility supply lines and the motor drive to prevent electricity at frequencies other than the nominal utility line frequency (50 Hz or 60 Hz) from being applied from the motor drive onto the supply lines. It is undesirable that such higher frequency signals be conducted by the supply lines as that might adversely affect the operation of other electrical equipment connected to those lines. In the case of a three-phase motor drive, a filter comprising one or more inductors and other components for each phase line has been used to couple the motor drive to the supply lines and attenuate the undesirable frequencies. Such inductors are wound on an iron core which adds substantial weight to the motor drive.
Thus, it is desirable to minimize the weight and size of the inductors used in the electrical supply line filters.